Duf format only works in C8.5 or newer.

Anyone still running C8 (or earlier) cannot use DUF files.

The nice thing was many vendors offered Poser files that worked like a champ in earlier versions of Carrara and Poser 9 (and earlier)

I am using C8.5 and have had trouble with DUF files - they might load, but the movable parts, e.g. doors, don't work.  I haven't tried very many, but I avoid DUF files altogether now.  The Poser format files almost always work seamlessly, and I'd rather create short animations than wrestle with compatibility problems.  I strongly doubt that DAZ is working to improve Carrara, and suspect that the programmers who could do it are long gone.